The present invention relates generally to the field of articles comprising a microporous layer. More particularly, this invention pertains to methods of preparing an article comprising a microporous layer in which a microporous layer is coated on a temporary carrier substrate and a substrate is then laminated to the microporous layer, prior to removing the temporary carrier substrate from the microporous layer. The present invention also pertains to articles, such as electrochemical cells, capacitors, fuel cells, ink jet printing media, and filtration media, prepared by such methods.
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
U.S. patent application Ser. No. 08/995,089 titled xe2x80x9cSeparators for Electrochemical Cells,xe2x80x9d filed Dec. 19, 1997, to Carlson et al. of the common assignee, describes microporous layers as separators for use in electrochemical cells in which microporous layers comprise a microporous pseudo-boehmite layer prepared by coating and drying a boehmite sol. The microporous pseudo-boehmite separators and methods of preparing such separators are described for both free standing separators and as a separator layer coated directly onto an electrode or another layer of the cell.
When a microporous layer, such as a microporous separator layer, is coated directly onto an electrode, such as onto the cathode, the microporous separator coating may require a relatively smooth, uniform surface on the electrode and also may require a mechanically strong and flexible electrode layer. For example, for a microporous pseudo-boehmite layer having a xerogel structure, these specific electrode surface and layer properties may be required to prevent excessive stresses and subsequent cracking of the xerogel layer during drying of the pseudo-boehmite coating on the electrode surface and also during fabrication and use of electrochemical cells containing the pseudo-boehmite xerogel layer.
Besides separator-coated electrodes and electrochemical cells, a large variety of other articles comprising a microporous layer may require a relatively smooth, uniform surface on a substrate to which the microporous layer is to be applied. Also, the substrate may need to be mechanically strong and flexible. For example, for a microporous xerogel layer as used in ink jet printing media, such as described, for example,in U.S. Pat. No. 5,463,178 to Suzuki et al., such smooth, uniform, and other substrate properties may be useful in preventing excessive stresses and subsequent cracking of the xerogel layer, particularly when its thickness is above 20 microns, and also useful in providing excellent image quality. Some of the desired substrates in ink jet printing media, such as canvas, cloth, non-woven fiber substrates, and some grades of paper, have very rough and non-uniform surfaces and are difficult to coat with the microporous xerogel layers which typically provide the premium ink jet image quality. One approach to overcome the surface deficiencies of the substrate is to pre-coat the substrate with a coating layer. This approach may reduce the surface roughness and non-uniformities, but involves the expense and complexity of an additional coating step, usually does not fully eliminate the surface deficiencies, and may negatively affect the ink jet imaging, such as by interfering with the microporosity and transport of liquids between the xerogel layer and the rough but porous substrate.
In another approach that may overcome the surface deficiencies of the substrate, the ink jet ink-receptive layer may be coated on a temporary carrier layer to form an ink jet ink printing media for imaging on an ink jet printer, as, for example, described in U.S. Pat. Nos. 5,795,425 and 5,837,375, both to Brault et al. Then, as part of a two step imaging process, the ink jet media is imaged on the ink jet printer followed by lamination of the imaged ink jet ink-receptive layer to a desired substrate and removal of the temporary carrier layer from the ink jet ink-receptive layer. This approach has the disadvantage of being a two-step imaging proess where the user may obtain excellent quality in the first imaging step, but then, after the effort and expense of imaging, the quality of the second lamination step may be unacceptable. Also, this two step imaging process requires the user to have the equipment for the second lamination step. It would be advantageous to have a one step imaging process for ink jet printing on ink jet ink printing media having rough, non-uniform substrates.
A method for preparing articles, such as electrochemical cells and ink jet printing media, which can avoid the foregoing problems often encountered with preparing articles comprising a microporous layer, particularly those comprising a microporous xerogel layer, would be of great value.
The present invention pertains to methods of preparing an article comprising a microporous layer, which methods comprise the steps of (a) coating a microporous layer on a temporary carrier substrate to form a microporous layer assembly, wherein the microporous layer has a first surface in contact with the temporary carrier substrate and has a second surface on the side opposite from the temporary carrier substrate; (b) laminating the second surface of the microporous layer to a substrate to form a microporous layer/substrate assembly; and (c) removing the temporary carrier substrate from the first surface of the microporous layer to form the article. In a preferred embodiment, the microporous layer comprises one or more microporous xerogel layers. In one embodiment, the microporous layer assembly further comprises one or more non-microporous coating layers, wherein the one or more non-microporous coating layers are in contact with at least one of the one or more microporous xerogel layers of the microporous layer. In one embodiment, one of the one or more microporous xerogel layers of the microporous layer is coated directly on the temporary carrier substrate. In one embodiment, one of the one or more non-microporous coating layers of the microporous layer assembly is coated directly on the temporary carrier substrate prior to coating the microporous layer, and the microporous layer is then coated on a surface of the one of the one or more non-microporous coating layers, which surface is on the side of the one of the one or more non-microporous coating layers opposite from the temporary carrier substrate, and further wherein the temporary carrier substrate is removed in step (c) from asurface of the one of the one or more non-microporous coating layers, which surface is on the side of the one of the one or more non-microporous coating layers opposite from the microporous layer. In one embodiment, one of the one or more non-microporous coating layers of the microporous layer assembly is coated after step (a) directly on the surface of the microporous layer, which surface is on the side of the microporous layer opposite from the temporary carrier substrate layer, prior to laminating to the substrate in step (b).
In a preferred embodiment, at least one of the one or more microporous xerogel layers comprises a xerogel material selected from the group consisting of pseudo-boehmites, zirconium oxides, titanium oxides, aluminum oxides, silicon oxides, and tin oxides. In one embodiment, the microporous layer comprises a microporous material prepared by vesiculation of an organic polymer layer, and wherein said vesiculation comprises a step of photolyzing or heating a gas forming compound. In one embodiment, the gas forming compound is an aromatic diazonium compound.
In one embodiment of the methods of preparing an article comprising a microporous layer of the present invention, the temporary carrier substrate is a flexible web substrate. Suitable web substrates include, but are not limited to, papers, polymeric films, and metals. In one embodiment, the flexible web substrate is surface treated with a release agent.
In one embodiment, the microporous layer assembly is a cathode/separator assembly, the substrate is an anode assembly, and the article is an electrochemical cell. The electrochemical cell may be a primary cell or a secondary cell.
In one embodiment, the microporous layer assembly is an ink jet ink-receptive coating assembly, the substrate is a flexible web substrate, and the article is an ink jet ink printing media.
In one embodiment, the microporous layer assembly is an ultrafiltration layer assembly, the substrate is a flexible web substrate, and the article is a filtration media.
In one embodiment, the microporous layer assembly is a separator assembly, the substrate is a first electrode assembly, and the article is a first electrode/separator assembly. In one embodiment, the methods further comprise the step of combining the first electrode/separator assembly with a second electrode assembly to prepare an electrochemical cell, a capacitor, or a fuel cell.
Another aspect of the present invention pertains to an article prepared by the methods of this invention, as described herein. In a preferred embodiment, the article is an ink jet ink printing media.
As will be appreciated by one of skill in the art, features of one aspect or embodiment of the invention are also applicable to other aspects or embodiments of the invention.